Structural, morphological, elastic, optoelectronic and thermoelectric properties of lead-free double perovskite Na2AgBiBr6 for photovoltaic applications: Experimental and DFT insight

Abstract

Herein, a lead-free double perovskite is synthesized utilizing an antisolvent recrystallization technique. The double perovskite Na₂AgBiBr₆ is studied in detail, including its crystal structure, stability, morphology, electronic, optical, and thermoelectric properties. X-ray diffraction (XRD) confirms the formation of Na₂AgBiBr₆ double perovskite and demonstrates remarkable structural stability. Crystals of uniform multifaceted Na₂AgBiBr₆ are seen by scanning electron microscopy (SEM). Polycrystalline-Na₂AgBiBr₆ crystals in a cubic ordered phase by the solution synthesis approach are ensured by TEM and electron diffraction analysis. Furthermore, energy-dispersive X-ray spectroscopy (EDX) mapping indicates the overlapping of Na, Ag, Bi, and Br elements and the uniform content of each element in the synthesized material. According to UV–vis spectroscopy, a band gap of 2.6 eV is observed. Further, the density functional theory (DFT) calculations suggested the structural as well as thermal stability acquired by tolerance factor and negative formation energy, respectively. DFT-predicted lattice parameter and band gap are verified by XRD and UV–vis spectroscopy, respectively. Elastic properties confirmed the mechanical stability, anisotropy, and ductile nature. The optical properties revealed the higher absorbance and low reflectivity in the energy range 0–6 eV. The thermoelectric attributes ensure the higher electrical conductivity and low thermal conductivity resulting in a figure of merit (ZT) value of 0.77. The outcomes of this research propose that the lead-free and eco-friendly Na₂AgBiBr₆ double perovskite holds considerable potential as absorber layer material for solar cells and for thermoelectric device applications.